This invention relates to flame-resistant materials, and particularly to foam (sponge) rubber backing materials, e.g. for carpet. Specifically, the invention provides a novel sponge rubber carpet underlay material highly resistant to burning.
The term "carpet" herein refers to natural or synthetic floor coverings. A common carpeting at the present time comprises a fabric base with yarn tufts extending upwardly from the base and forming the pile of the carpet. Various methods are known to those skilled in the art for constructing the base and attaching pile yarns to it.
Ordinarily, an underlay material, generally a foam rubber material, is used as a base over which carpet is laid to provide greater resilience and to cushion the carpeting material. Foamed or sponge rubber underlays are well known, particularly those prepared from styrene-butadiene rubber (hereinafter for convenience called SBR). Such rubber underlays are not intrinsically fire-resistant, howwever, and it is known to incorporate polyvinyl chloride therein to impart flame resistance to the underlay. Unfortunately, addition of untreated polyvinyl cloride to a styrene-butadiene latex normally results in the latex being not self-supporting and therefore difficult to process. On the other hand, in the preparation of a sponge underlay of SBR wherein a solids system (rather than a latex) is used, the underlay is prepared by calendaring particulate SBR material, stripping the resulting self-supporting continuous sheet from the calendar and feeding that sheet to other mechanical processing means, e.g. conveyor belts, cooling rollers and calendars. Addition of a vinyl chloride polymer, e.g. polyvinyl chloride, to SBR in such a process similarly destroys the "green strength" of the rubber, thereby destroying its self-supporting characteristic. The loss of that characteristic is significant because the sheet of rubber prepared in a calendaring process must be self-supporting so that the sheet can emerge from a calendar and retain its integrity over a short distance during which it is unsupported while being fed into a subsequent roller or calendar. Thus it is a significant problem in the carpeting industry to prepare a sponge rubber underlay, prepared by a calendaring process, which can be rendered fire resistant by addition of a vinyl chloride polymer without substantial loss of green strength of the underlay material.